The present invention relates to the construction of electro-mechanical devices, most commonly known as switched reluctance motors. These motors can translate electrical energy into power and torque through the use of electromagnetic structures built around a fixed stator and an internal rotating rotor. In general, the stator of the prior art is generally comprised of a plurality of discreet lobes or poles, which extend inwardly towards the rotor. The associated rotor is also constructed of magnetic materials having a plurality of discreet poles that are constructed to extend outwardly toward the stator poles. To ensure self-starting, the object of the switched reluctance motor design is to ensure that one stator pole always overlays one rotor element, resulting in the need to have a different pitch between the number of stator and rotor poles.
Energizing in sequence the electromagnetic coils associated with each opposing pair of stator pole during each energizing cycle, creates a magnetic field that will draw an appropriately positioned rotor pole into alignment with one of the energized stator poles creating rotation and torque. As a consequence of having only one pole pair in the correct position at any given time (due to the different pitch between the number of stator and rotor poles) during the energizing sequence, relatively low torque is available. Manufacturers therefore will normally oversize switched reluctance motors relative to their steady-state operation performance leading to structural distortion of the motor casing, vibration, noise, large torque ripple effects in the torque output of the machine and low motor efficiency throughout the motor's operating range.
U.S. Pat. No. 5,365,137 of Richardson et al. identifies an arrangement incorporating an equal number of stator and corresponding rotor poles which can all be energized simultaneously for purposes of generating higher motor torque without the excessive torque ripple and distortion of the motor casing commonly found with other designs. With this arrangement, the motor is divided into a plurality of segments or stages, with each stage having successive rotor poles angularly displaced to permit self-starting. By energizing all of the stator poles within a stage and having each stage energized in sequence, the motor is inherently self-starting resulting in producing higher torque, lower torque ripple, less vibration and noise.
Other prior art includes U.S. Pat. No. 5,969,454 which illustrates rotor sections which are angularly offset.
Other rotary electric motor arrangements are shown in U.S. Pat. Nos. 6,927,524, 6,762,524, 6,617,746, 5,433,282, 5,727,560, 5,365,137
Switching circuits are shown in U.S. Pat. Nos. 5,115,181, 5,404,091, 5,012,177
U.S. Pat. Nos. 5,545,964 and 4,143,308 show control systems and methods of controlling a switched reluctance generator. U.S. Pat. No. 7,009,360 discloses a method of controlling a switched reluctance motor. U.S. Pat. No. 6,509,710 relates to a switched reluctance motor which is controlled by signals indicating the angular position of the rotor. U.S. Pat. Nos. 7,250,734 and 6,864,658 also illustrate a method of controlling a switched reluctance machine.
U.S. Re. 31,950 discloses that the pole shoes are skewed in relation to the rotor axis. Moreover, U.S. Pat. No. 4,670,696 illustrates laminated rotors which are skewed along the axial length of the rotor relative to its axis of rotation.
Cooling systems for switched reluctance motors are disclosed in U.S. Pat. Nos. 7,049,716, 7,193,342, 6,815,848, 7,244,110, 7,156,195, 6,897,584, 7,091,635, 6,300,693, 5,372,213, 2,824,983, 3,663,127, 3,518,468, 4,743,176 and 5,222,874.
U.S. Pat. No. 6,153,956 discloses circuitry which includes a first calculating means which includes a look-up table wherein the look-up table provides a relationship between the reference flux linkage value, the phase current and the shaft angle.
U.S. Pat. No. 7,230,361 relates to a method for determining a design of electrical devices based on an analysis of key design equations which permits design of an axial airgap machine with optimized torque at a given speed.
U.S. Publications 2005/0162031 and 2005/0099082 illustrate poles that are skewed or circumferentially displaced.
The present invention addresses the need for a motor/generator that produces higher torque, lower torque ripple, less vibration and noise while incorporating improved design techniques to optimize the arrangement, construction, performance, control and cooling.